Mixed oxides of Group 3 (including the Lanthanides and Actinides) and Group 4 metals are known to be useful in catalyzing oxidation-reduction reactions such as exhaust gas purification.
The use of such catalysts in the purification of exhaust gases, particularly gases produced by an internal combustion engine, have been described, for instance, in U.S. Pat. Nos. 5,478,543; 5,518,699; 5,532,198; 5,580,536; 5,582,785; 5,607,892; 5,712,218; 5,747,401; 5,908,800; 6,133,194; 6,150,299; 6,255,242; 6,291,719; 6,319,876; 6,506,705, and 6,605,565
Various catalyst have been proposed for the decomposition of ethers, have been described, for instance, in U.S. Pat. Nos. 4,691,073; 4,254,290; 4,320,232; 4,521,638; 4,398,051; 4,357,147. “Production D'Isobutene de Haute Pureté par Décomposition du MTBE” by P. B. Meunier et al. in Revue de L'Institut Francais du Petrole, vol. 46, No. 3, May 19991, pages 361 to 387, U.S. Pat. Nos. 5,254,785, 5,177,301, 5,171,920 and Japanese Published Patent Application No. JP-A-06072904.
Unpublished International Application No. PCT/US2004/041546 discloses a process for selectively converting a dialkyl ether to the corresponding alkene and alkanol, the process comprising contacting a feed containing at least one dialkyl ether with a catalyst comprising an acidic mixed metal oxide having the following composition:XmYnZpOqwhere X is at least one metal selected from Group 4 of the Periodic Table of Elements, Y is at least one metal selected from Group 3 (including the Lanthanides and Actinides) and Group 6 of the Periodic Table of Elements and Z is at least one metal selected from Groups 7, 8, and 11 of the Periodic Table of Elements; m, n, p and q are the atomic ratios of their respective components and, when m is 1, n is from 0.01 to 0.75, p is from 0 to 0.1, and q is the number of oxygen atoms necessary to satisfy the valence of the other components. The mixed oxides preferably contain sulfur, typically present in an amount of up to 5 wt %, such as up to 1 wt %, of the final mixed oxide composition. The mixed oxides can prepared by impregnation or by co-precipitation from a liquid mixture containing a source of Group 4 metal ions and a source of Group 3 and/or Group 6 metal ions.
One of the key challenges in developing this technology is the development of a catalyst that selectively converts the ether to the alcohol without subsequently dehydrating the alcohol to the corresponding olefin. The catalytic performance of the ceria-zirconia catalyst is influenced by the method of making of the ceria-zirconia mixed metal oxide, and factors such as the ceria content, pH of precipitation, gel aging, and calcination temperature all affect the catalyst performance. The present inventors, however, have discovered a cerium-sulfur-zirconium catalyst that has the desired level of activity and selectivity for this reaction.